Use Model.all instead of Model.scope deprecated in Rails 4.

Simple little fix to remove a deprecation warning under Rails 4.

I haven't researched backwards compatibility with Rails 3.x or how to possibly offer it, but I'd be glad to discuss it here.

More about this here: http://blog.remarkablelabs.com/2012/12/what-s-new-in-active-record-rails-4-countdown-to-2013